Plug welding experiment is carried out with ER308 welding wires for1.5 mm ferritic stainless steel 1.4003 and 3 mm weathering resistance steel. The microstructure analysis

microhardness test and pulsating tensile fatigue test of plug welding joints are carried out. The result shows that the microstructure of nugget zone of plug welding joint is δferrite+austenite

the microstructure of heat-affected zone（HAZ） of stainless steel 1.4003 is granular ferrite

grain size is 3～4 class

and the grain growth phenomenon is relatively obvious. The microstructure of HAZ of Q345 NQR2 steel is pearlite + a small amount of ferrite. The hardness of nugget zone is the highest

and the hardness of side HAZ of stainless steel 1.4003 is slightly lower than that of the nugget zone

while the hardness of side HAZ of Q345NQR2 significantly increases. Under the condition of cycle life of 1 ×10

7

the median fatigue strength of plug welding joint is 1.675 kN

and the fatigue cracks start at the edge of nugget zone between the two plates

the main reason is that this place is affected by both tensile stress and shear stress.